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Latest QZSS+GPS Almanac DataAlmanac

Latest QZSS+GPS Almanac DataOutline

Almanac is a set of data that depicts the trajectory of each satellite.(*revised:2011/02/07)

It is used to calculate the satellite's approximate position.

Almanacs for QZSS and GPS are available at this site.

Latest QZSS+GPS Almanac DataDefinition

ID

PRN of the SVN

Health

The health of the satellites

In the QZSS Almanac, health of the satellites are written in the form of 1bit + 5bits in decimal, as defined in the IS-QZSS. The "0" is placed when the signal is available, "1" when not available.(*revised:2011/07/15)

5bit health definition
1st bit(MSB)L1C/A signal health(*)
2nd bitL2C signal health(*)
3rd bitL5 signal health(*)
4th bitL1C signal health(*)
5th bitLEX signal health(for GPS, always fixed to "1")

(*)signals not broadcasted are fixed to "1"

Refer the IS-QZSS 5.1.2.1.3.3 for more information.

Note that the definition is not identical with the IS-GPS-200E.

Eccentricity

This shows the amount of the orbit deviation from circular (orbit).

It is the distance between the foci divided by the length of the semi-major axis (our orbits are very circular).

QZSS will give a larger eccentricity than GPS due to its ellipse orbit.

Time of Applicability

The number of seconds in the orbit when the almanac was generated. Kind of a time tag.

Orbital Inclination

The angle to which the SV orbit meets the equator(QZSS is at approximately 41 degrees, GPS at 55 degrees).

The number is written in radian : * 180/π = the inclination in degrees.

Rate of Right Ascension

Rate of change in the measurement of the angle of right ascension.(Right Ascension is an angular measurement from the vernal equinox.)(*revised:2011/01/24)

SQRT(A) Square Root of Semi-Major Axis

This is defined as the measurement from the center of the orbit to either the point of apogee or the point of perigee.

Right Ascension at Time of Almanac (TOA)

Geographic longitude of the ascending node of the orbit plane at the weekly epoch.(*revised:2011/01/24)

Argument of Perigee

An angular measurement along the orbital path measured from the ascending node to the point of perigee, measured in the direction of the SV's motion.

Mean Anomaly

Angle (arc) traveled past the longitude of ascending node (value = 0±180 degrees).

If the value exceeds 180 degrees, subtract 360 degrees to find the mean anomaly.

When the SV has passed perigee and heading towards apogee, the mean anomaly is positive.

After the point of apogee, the mean anomaly value will be negative to the point of perigee.

af0

SV clock bias in seconds.

af1

SV clock drift in seconds per seconds.

Week

GPS week (0000–1023), every 7 days since 1999 August 22.

Latest QZSS+GPS Almanac DataLatest Almanac

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